Can we farm without animals and manure?

The objection

“Farming needs animals. Manure keeps soil fertile, and grazing is the only way to get food from marginal land that crops can’t use.”

The answer

The objection starts from two true things. Manure is a useful fertiliser, and about two-thirds of the world’s pasture is unsuitable for growing crops, according to Our World in Data (2021) [1]. Neither makes animals necessary, because manure moves nutrients around without creating any, and grazing land that can’t be cropped gives back very little food for the space it takes.

Can crops be grown without animal manure?

Crops can be grown without animal manure, because the nitrogen it supplies can come from legumes grown in the rotation instead. Manure hands back what the animals ate: a 1993 Purdue University extension leaflet in the US said livestock excrete 70 to 80% of the nitrogen, 60 to 85% of the phosphorus and 80 to 90% of the potassium in their feed [2]. By its reckoning, the manure from 100 acres of maize fed to livestock may hold enough phosphorus and potassium for about 75 acres [2]. The nutrients were in the crop before they were in the animal. A 2002 conference paper on two long-term trials in England found that stockless rotations with one or two years of red clover grown as green manure got enough nitrogen from it for three or four years of arable crops [3]. Over 11 years at one site and five at the other, yields varied a lot from year to year but showed no sign of declining, and were generally at or above the average for organic farms [3]. Soil phosphorus and potassium stayed at levels that did not hold crops back, though perennial weeds were the biggest problem the trials ran into [3].

Where manure is harder to replace is in keeping up the soil’s organic matter. In the Gladbacherhof long-term organic trial, reported in 2014 after two six-year rotations, only the system that grew fodder legumes and spread cattle manure held or possibly raised its soil organic matter [4]. A stockless system with a legume ley as green manure barely held its level, and one relying on catch crops and straw lost a considerable amount [4]. The researchers concluded that fodder legumes are a crucial prerequisite for keeping up soil organic matter in stockless organic farming, unless new approaches, such as swapping fodder for manure with livestock farms, recirculating residues from biogas plants or intercropping to grow far more legumes, provide a full substitute [4]. Veganic farms, which replace manure with composts, mulches, green manures and crop rotation, do exist in the United States, though the 19 in a 2021 study were all small, with ten acres or less under cultivation [5]. The study’s authors argued for more research into soil health and fertility in plant-based systems [5].

What about land that can only be grazed?

Grazing land that can’t grow crops produces very little food for the space it takes. Animal products use 83% of the world’s farmland and supply 18% of its calories and 37% of its protein, in the University of Oxford’s summary [6] of Poore and Nemecek’s 2018 study of 38,700 farms [7]. Lamb and beef from beef herds, the meats that rely on pasture [1], need about 185 and 164 square metres of land for every 100g of protein in the same study’s data, more than any other food in it and roughly 50 to 55 times the 3.4 square metres for peas [8]. Poore and Nemecek also found that even the lowest-impact animal products typically do more environmental damage than the plant foods that could replace them [7].

Followed through, the marginal-land argument points the other way. A plant-based food system would need about 1 billion hectares of farmland instead of 4.1 billion, according to Our World in Data (2021) [1]. Hayek and colleagues (2021) estimated that restoring ecosystems on the land freed by a shift to plant-based diets by 2050 could draw down 332 to 547 billion tonnes of CO2, equal to 99 to 163% of the carbon dioxide budget for a two-in-three chance of limiting warming to 1.5°C [9]. That is the trade the objection leaves out, since keeping cattle on land also keeps it from growing back. Some habitats do need to be grazed: a third of those protected under the EU’s Habitats Directive depend on extensive grazing, according to the European Environment Agency (2026) [10]. Its preliminary estimate is that about 10 to 15% of the EU’s cattle, sheep and goats would be enough to graze them if spread to the right places, and it says wild grazers can do the job too [10]. What the freed land could become is covered in what would happen to the farmland if everyone went vegan.

The claim that grass-fed and regenerative grazing stores enough carbon in the soil to cancel out the cattle has its own answer.